1. Field of the Invention
The present invention relates to a main circuit switching apparatus disposed between a generator and a main transformer in a power plant.
2. Description of the Related Art
FIG. 4 is a single-line diagram of a power plant, and shows one which is generally adopted conventionally. In the drawing, G denotes a generator; M.Tr denotes a main transformer; H.Tr denotes an in-house transformer; S.Tr denotes a starting transformer; S1-S4 denote circuit breakers; B denotes a bus; and L1 and L2 denote transmission lines. The generator G and the main transformer M.Tr are directly connected to each other, and when the generator G is started, electric power for starting the generator G is supplied to the bus B via the starting transformer S.Tr, and the generator G is connected to the transmission line L1 via the main transformer M.Tr by means of the breaker S1 in synchronism with the voltage of the transmission line L1.
Recently, a low-tension synchronization system such as the one shown in a single-line diagram in FIG. 5 has come to be adopted instead of the above-described high-tension synchronization system.
In this case, a main circuit switching apparatus A is installed for the generator G. FIG. 6 shows the details of the main circuit switching apparatus A. In the drawing, B denotes a main circuit breaker; C denotes a main circuit disconnecting switch; D denotes a breaker-side grounding device; and E denotes a disconnecting switch-side grounding device. Here, if all of the main circuit breaker B, the main circuit disconnecting switch C, and the breaker-side and disconnecting switch-side grounding devices D and E are arranged by being integrated as a unit rather than being collected together as individual single devices, the total installation area can be made small, and the production cost can be lowered, so that the main circuit switching apparatus of this integrated type is tending to be adopted on an increasing scale.
FIG. 7 is a cross-sectional view of a main circuit switching apparatus of the integrated type which is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-306282. In the drawing, reference numeral 1 denotes a breaking section; 2, an insulating barrel; 3, a breaking section fixed-side conductor fixed to one end of the insulating barrel 2; 4, a breaking section movable-side conductor attached to the other end of the insulating barrel 2; 5, a fixed contact fixed to the breaking section fixed-side conductor 3; and 6, a movable contact attached to the breaking section movable-side conductor 4 in such a manner as to be capable of coming into contact with and moving away from the fixed contact 5. The insulating barrel 2, the breaking section fixed-side conductor 3, the breaking section movable-side conductor 4, the fixed contact 5, and the movable contact 6 constitute the breaking section 1.
Numeral 8 denotes a disconnecting section; 9, a disconnecting section fixed-side conductor formed integrally with the breaking section movable-side conductor 4, a partition wall 10 being provided between the disconnecting section fixed-side conductor 9 and the breaking section movable-side conductor 4, and an insulating gas such as sulfur hexafluoride being sealed in on the breaking section 1 side. Numeral 11 denotes a disconnecting section movable-side conductor disposed by being spaced apart from the disconnecting section fixed-side conductor 9; and 12 denotes a movable conductor attached to the disconnecting section movable-side conductor 11 in such a manner as to be capable of coming into contact with and moving away from the disconnecting section fixed-side conductor 9. The disconnecting section fixed-side conductor 9, the disconnecting section movable-side conductor 11, and the movable conductor 12 constitute the disconnecting section 8.
Numeral 14 denotes a first grounding conductor for grounding the breaking section fixed-side conductor 3; and 15 denotes a second grounding conductor for grounding the disconnecting section movable-side conductor 11.
Numeral 16 denotes a supporting rack; 17 and 18 denote first and second supporting insulators for supporting on the supporting rack 16 an integrated portion formed by the breaking section 1 and the disconnecting section fixed-side conductor 9; and 19 denotes a third supporting insulator for supporting on the supporting rack 16 the disconnecting section movable-side conductor 11 and the movable conductor 12.
Numeral 21 denotes a breaking-section operating device which has a first insulated operating rod 22 to operate the movable contact 6 of the breaking section 1. Numeral 23 denotes a disconnecting-section operating device which has a second insulated operating rod 23 to operate the movable conductor 12 of the disconnecting section 8. Numerals 25 and 26 denote first and second grounding-section operating devices for operating the first and second grounding conductors 14 and 15.
On the supporting rack 16, the breaking section 1 and the disconnecting section 8 are arranged in the order of the breaking section fixed-side conductor 3, the breaking section movable-side conductor 4, the disconnecting section fixed-side conductor 9, and the disconnecting section movable-side conductor 11. The respective operating devices are accommodated and fixed in the supporting rack 16 in the order of the first grounding-section operating device 25, the breaking-section operating device 21, the disconnecting-section operating device 23, and the second grounding-section operating device 26.
In the above-described manner, the main circuit switching apparatus A is formed in which the respective devices B, C, D, and E shown in FIG. 6 are integrated as a unit.
The conventional main circuit switching apparatus of the integrated type configured as described above is advantageous in terms of the reduction of the installation area and the lowering of production cost as compared with the case where the breakers, disconnecting switches, and grounding devices are respectively formed as single devices. However, the conventional main circuit switching apparatus of the integrated type has the following problems.
(i) In order for the respective operating devices to operate properly, it must be ensured that the operating devices, the grounding conductors, and the supporting insulators do not interfere with each other. To avoid the interference, it is necessary to elongate the axial length L of the main circuit switching section and dispose the grounding devices on opposite end sides thereof, with the result that the integration of the grounding devices leads to the large size of the apparatus. Meanwhile, it is also conceivable to dispose the grounding-section operating devices in a space which is produced between the breaking-section operating device and the disconnecting-switch operating device so as not to elongate the length L. However, the arrangement of the operating devices at that time does not conform to the same order as that of the electrical arrangement of the main circuit switching apparatus such as the one shown in FIG. 6 in which the grounding devices are disposed at opposite ends of the main circuit breaking section and the main circuit disconnecting section which are connected in series. Since there is a possibility of causing erroneous confirmation and erroneous operation, such an arrangement is not preferable.
(ii) Since the main circuit switching apparatus is mechanically divided into two portions, i.e., one portion in which the breaking section and the disconnecting section fixed-side conductor are integrated and another portion including the disconnecting section movable-side conductor and the movable conductor, it is necessary to respectively insulate and support these two portions independently. As for the former portion between them, since the weight of the disconnecting section fixed-side conductor is much lighter than the weight of the breaking section, the position of its center of gravity is substantially not different from the position of the center of gravity of the breaking section alone, and is located on the insulating barrel of the breaking section, so that it is difficult to provide insulation and support at one location in the vicinity of the position of the center of gravity. For this reason, insulation and support are provided at two locations on the breaking section movable-side conductor and the breaking section fixed-side conductor. This means that two creepage insulation portions are present for the breaking section and the disconnecting section fixed-side conductor with respect to the ground, which leads to the lowering of electrical reliability, and increases the number of component parts, resulting in higher cost.
(iii) Since the disconnecting section fixed-side conductor which comes into contact with and moves away from the movable conductor is provided on the disconnecting section side, it is difficult to effect inspection from the outside on the state of contact in a state in which the disconnecting switch is on.
If cases where the low-tension synchronization system is adopted increase as in the recent years, there have been increasing demands for reducing the installation space required for installing the main circuit switching apparatus, lowering the producing cost, and providing the main circuit switching apparatus which is highly reliable, facilitates maintenance and inspection, and has good operational efficiency. In particular, in underground power plants where the installation space is limited, or in the case of independent power producer (IPP) where the operation is undertaken by users for whom electrical knowledge is not required as a special field, these demands have been increasingly strong.